The introduction of gaseous source materials into chemical vapor deposition (CVD) reactors is a critical part of the CVD process. If the reactant is stable in gaseous form at operating pressures and temperatures, it can be metered into the CVD reactor directly from a storage container. If it is stable in liquid form, it can be evaporated at a controlled rate to produce the gaseous reactant for the CVD process.
In many cases, however, a gaseous or liquid source is either not available or not useable in the process desired. Hence, a volatile source is often generated by chemical reaction or volatilization. At present, chemical generation of a volatile source gas is accomplished commercially by the use of a reactor external to the CVD apparatus. This technique offers the advantage of independent control of the source gas reaction conditions, but requires the use of an additional furnace and heated lines to the CVD reactor to prevent precipitation of the gaseous product. Apart from the added expense, this method has inherent problems, in that precipitate can build up in and eventually clog gas lines, or can disrupt the overall process.
The invention described herein and recited in the appended claims controls such precipitate build-up by providing one or more containers, or internal reactors, disposed within the CVD reactor for the generation of one or more source gases. The internal reactor utilizes heat from the CVD furnace, thereby reducing cost and simplifying the overall process. Additionally, such an internal reactor assembly can be used to generate simultaneously any number of source gases while controlling the relative quantity of each gas produced. The simultaneous generation, in turn, contributes to pre-mixing of the source gases, and results in the growth of materials, for example composite or multiphase coatings, of improved quality.